(a) Field of the Invention
The present invention relates to an automatic transmission powertrain. More particularly, the present invention relates to an automatic transmission powertrain in which two single pinion planetary gearsets are combined in a simple manner to realize a primary shift portion and a secondary shift portion such that a length of the powertrain is minimized, and in which a one-way clutch is used for 1⇄2, 2⇄3 and 4⇄2 shifting, thereby greatly improving shift feel.
(b) Description of the Related Art
A transmission control unit included in the automatic transmission automatically controls a shift ratio according to changes in vehicle speed and load. A planetary gearset is used as a multi-stage gearshift mechanism in the transmission control unit.
The planetary gearset generally includes an input element for receiving engine torque; an output element for transmitting the engine torque to a final reduction gear after the torque has undergone shifting; and a reaction element for enabling the engine torque received by the input element to be transmitted to the output element after being shifted to a predetermined range. The output element is typically fixedly connected to the final reduction gear. However, since the input element is varied, the input element is connected to an element that transmits the engine torque with a friction element interposed therebetween. For the same reason, the reaction element is connected to a transmission housing with a friction element interposed therebetween.
A significant number of conventional automatic transmission powertrains such as described above have been disclosed. A powertrain can have a variety of different structures including a structure in which planet carriers are interconnected, a structure in which a common sun gear is used and a planet carrier and a ring gear are directly connected, a structure in which a planet carrier and a ring gear are directly connected, and many more.
It is an object of the present invention to provide an automatic transmission powertrain in which two planetary gearsets are combined in a simple manner to realize a primary shift portion and a secondary shift portion such that a length of the powertrain is minimized, and in which a one-way clutch is used for 1⇄2, 2⇄3 and 4⇄2 shifting, thereby greatly improving shift feel.
To achieve the above object, the present invention provides an automatic transmission powertrain comprising a torque converter acting as a fluid link between an engine and a transmission, the torque converter outputting rotational power to an input shaft of the powertrain; a primary shift portion provided on a first shaft, a long axis of which is aligned with a long axis of the input shaft, the primary shaft portion being selectively connected to the input shaft to receive rotational power; a secondary shift portion provided on a second shaft, the second shaft being parallel to the first shaft with a predetermined gap therebetween, and the secondary shift portion being connected to the primary shift portion via two power transmitting paths to transmit power to an output shaft of the powertrain; a power transmitting means for transmitting rotational power of the primary shift portion to the secondary shift portion; a brake means for operating operational elements of the primary shift portion and the secondary shift portion as reaction elements; a clutch means for selectively transmitting power to operational elements of the primary shift portion; and a non-synchronous shift means for operating during 1⇄2, 2⇄3 and 4⇄2 shifting. According to a feature of the present invention, the primary shift portion is a first planetary gearset, a ring gear and a sun gear which are selectively connected to the input shaft through the clutch means.
According to another feature of the present invention, the secondary shift portion is a second planetary gearset, a ring gear of which is fixedly connected to the output shaft.
According to yet another feature of the present invention, the power transmitting means comprises a first power transmitting gear connected to a planet carrier of the first planetary gearset; a second power transmitting gear meshed with the first power transmitting gear, and connected to the ring gear of the second planetary gearset and the output shaft; a third power transmitting gear provided on the first shaft and fixedly connected to the sun gear of the first planetary gearset; and a fourth power transmitting gear meshed with the third power transmitting gear, fixedly connected to a sun gear of the second planetary gearset, and provided on the second shaft.
According to still yet another feature of the present invention, the brake means comprises a first brake provided between the second shaft and a transmission housing; a second brake provided between the first shaft and the transmission housing with elements of the non-synchronous shift means being interposed between the second brake and the first shaft; and a third brake provided between the first shaft and the transmission housing.
According to still yet another feature of the present invention, the clutch means comprises a first clutch selectively connecting the ring gear of the first planetary gearset and the input shaft; a second clutch selectively connecting the sun gear of the first planetary gearset and the input shaft; and a third clutch selectively connecting a sun gear and a planet carrier of the second planetary gearset.
According to still yet another feature of the present invention, the non-synchronous shift means comprises a first one-way clutch interposed between the second shaft and the transmission housing, the first one-way clutch operating in a first speed to enable an element of the second planetary gearset to act as a reaction element; and a second one-way clutch interposed between the first shaft and the second brake, the second one-way clutch operating in a second speed to enable an element of the first planetary gearset to act as a reaction element during operation of the second brake.